In the field of wireless communications, Long Term Evolution (LTE) networks provide User Equipment (UE) with Internet access and voice calling services. The voice calling service is referred to as Voice over LTE (VoLTE). LTE networks often use an Internet Multimedia Subsystem (IMS) to control these VoLTE sessions. When the UE registers on the LTE network, the LTE network assigns an IMS Proxy Call Session Control Function (P-CSCF) server to the UE. The UE then registers for VoLTE service with the IMS P-CSCF.
The UE may engage in wireless voice calls over the LTE network under the control of IMS. Unfortunately, the UE may lose wireless signal strength on the LTE network and change to a different wireless access network. If a VoLTE session is active for the UE, then the new wireless access network will contact an Access Transfer Control Function (ATCF) or an Emergency Access Transfer Function (EATF) in IMS to control the access network transfer for the voice session.
To prepare for these access transfers, numerous access network nodes need to have current contact information for the IMS ATCFs and EATFs on a per-session and per-UE basis. If the LTE network changes the P-CSCF for a UE during LTE registration, then the ATCF/EATF for the UE also changes since P-CSCFs and ATCF/EATFs are individually paired. The current technique for session transfer between networks is not efficient and is not effective.